The fate of intertidal microphytobenthos carbon: an in situ ¹³C-labeling study

At two intertidal sites (one sandy and one silty, in the Scheldt estuary, The Netherlands), the fate of microphytobenthos was studied through an in situ 13C pulse- chase experiment. Label was added at the beginning of low tide, and uptake of 13C by algae was linear during the whole period of tidal exposure (about 27 mg m-2 h-1 in the top millimeter at both sites). The 13C fixed by microphytobenthos was rapidly displaced toward deeper sediment layers (down to 6 cm), in particular at the dynamic, sandy site. The residence times of microphytobenthos with respect to external losses (resuspension and respiration) were about 2.4 and 5.6 d at the sandy and silly stations, respectively. The transfer of carbon from microphytobenthos to benthic consumers was estimated from the appearance of 13C in bacterial biomarkers, handpicked nematodes, and macrofauna. The incorporation of 13C into bacterial biomass was quantified by carbon isotope analysis of polar lipid derived fatty acids specific for bacteria. The bacterial polar lipid-derived fatty acids (i14:0, i15:0, a15:0, i16:0, and 18:1 omega 7c) showed rapid, significant transfer from benthic algae to bacteria with maximum labeling after 1 d. Nematodes became enriched after 1 h, and 13C assimilation increased until day 3. Microphytobenthos carbon entered all heterotrophic components in proportion to heterotrophic biomass distribution (bacteria > macrofauna > meiofauna). Our results indicate a central role for microphytobenthos in moderating carbon flow in coastal sediments

Seasonal Growth Rate of the Sponge Haliclona oculata (Demospongiae: Haplosclerida)

The interest in sponges has increased rapidly since the discovery of potential new pharmaceutical compounds produced by many sponges. A good method to produce these compounds by using aquaculture of sponges is not yet available, because there is insufficient knowledge about the nutritional needs of sponges. To gain more insight in the nutritional needs for growth, we studied the growth rate of Haliclona oculata in its natural environment and monitored environmental parameters in parallel. A stereo photogrammetry approach was used for measuring growth rates. Stereo pictures were taken and used to measure volumetric changes monthly during 1 year. Volumetric growth rate of Haliclona oculata showed a seasonal trend with the highest average specific growth rate measured in May: 0.012 ± 0.004 day−1. In our study a strong positive correlation (p < 0.01) was found for growth rate with temperature, algal biomass (measured as chlorophyll a), and carbon and nitrogen content in suspended particulate matter. A negative correlation (p < 0.05) was found for growth rate with salinity, ammonium, nitrate, nitrite, and phosphate. No correlation was found with dissolved organic carbon, suggesting that Haliclona oculata is more dependent on particulate organic carbon

Influence of phosphorus on copper sensitivity of fluvial periphyton: the role of chemical, physiological and community-related factors

The influence of eutrophication of fluvial ecosystems (caused by increased phosphorus concentrations) on periphyton Cu sensitivity is explored from a multi-scale perspective, going from the field to the laboratory. The study design included three tiers: a field study including the characterization of land use and the ecological state of the corresponding river sections in the Fluvià River watershed, an experimental investigation performed with natural periphyton from the previously studied stream sites in indoor channels, and finally a culture study in the laboratory. Results showed that differences in copper sensitivity of natural periphyton communities followed the gradient of nutrient concentration found in the field. Results from the culture experiments demonstrated that both, P-conditions during growth and P-content in the media are important factors modulating the toxicological response of algae to Cu. The observations from this study indicate that the ecological effects of metal pollution in rivers might be obscured by eutrophication

Microphytobenthos of Arctic Kongsfjorden (Svalbard, Norway): biomass and potential primary production along the shore line

During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline of Kongsfjorden (Svalbard, Norway) at ?5 m water depth and at two stations at five different water depths (5, 10, 15, 20, 30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment cores under controlled light (ca. 100 ?mol photons m?2 s?1) and temperature (2–4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down to 30 m showed high biomass of up to 317 mg chl a m?2. In spite of increasing water depth, no significant trend in “photoautotrophic active biomass” (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from ?5 to 30 m water depth exhibited variable rates of net production from ?19 to +40 mg O2 m?2 h?1 (?168 to +360 mg C m?2 day?1) and gross production of about 2–62 mg O2 m?2 h?1 (17–554 mg C m?2 day?1), which is comparable to other polar as well as temperate regions. No relation between photoautotrophic biomass and gross/net production values was found. Microphytobenthos demonstrated significant rates of primary production that is comparable to pelagic production of Kongsfjorden and, hence, emphasised the importance as C source for the zoobenthos

Estimating primary production rates from photosynthetic electron transport in estuarine microphytobenthos

Microphytobenthos primary production was measured using C fixation and compared with production estimates based on measurements on intact cores using variable chlorophyll fluorescence with a PAM (pulse-amplitude-modulated) fluorometer at a number of different sites on intertidal flats in the Westerschelde and Oosterschelde estuaries (The Netherlands). We observed a linear relationship between the minimal fluorescence, F-0, and the chlorophyll a content of the sediments, but the relationship was quite noisy, which was partly due to a vertical scale mismatch between the depth of sampling (1 mm) and the measuring depth the of PAM fluorometer (100 to 200 mum) On most sites, C fixation was a linear function of photosystem II electron transport (ETR, obtained from PAM measurements), although for Stn B, a relatively silty site on the Molenplaat, an intertidal flat in the Westerschelde, the agreement between C fixation and ETR was often non-linear at irradiances saturating C fixation. This was sometimes observed for some of the other stations as well. The differences at high irradiance might be related to vertical migration of epipelic diatoms, optical properties of the sediment or alternative electron accepters. A conversion factor was calculated, allowing estimation of C fixation from ETR measurements. This conversion factor was not different for the different stations and no clear seasonal influence was observed, although the conversion factor could vary within hours. The seasonally averaged conversion factor for all stations and each site was used to calculate areal rates of production and compared with primary production estimates obtained from the C fixation measurements. It appeared that the PAM-based estimates gave a good prediction of the (potential) C fixation, with the exception of a number of dates for Molenplaat Stn B. This demonstrates that the variable fluorescence technique can become, after further calibration with C-14 for Other shallow sediments, a very useful tool in production studies, and can be instrumental in obtaining a good spa; tial coverage of primary production, which remains very difficult due to the patchiness in microphytobenthos biomass and production. [KEYWORDS: chlorophyll fluorescence; photosynthetic electron transport; C fixation; micro-phytobenthos; primary production; tidal flats Variable chlorophyll fluorescence; photosystem-ii; benthic microalgae; oxygen evolution; quantum yield; phytoplankton photosynthesis; marine-phytoplankton; natural assemblages;incident irradiance; charge separation]